Hello!
The correct answer is C.
As we should know, a neutron star is a small cluster of neutrons. It is neither middle aged or able to burn hydrogen.
A white dwarf is a “mock planet” and has no impact on hydrogen.
A pulsar is a form of a neutron star, making C the only possible answer.
Main sequence stars are both middle aged and able to use hydrogen to form other substances.
I hope I helped!
